The aims of this research are: 1) to partition the genetic and environmental contributions to the tendency for blood pressure to increase with age; and 2) to examine the relationship between estimates of sodium and postassium intake in free-living families and the familial aggregration of blood pressure. The research design utilizes the power of the genetic analysis that can be derived from the study of the families (spouses and children) of adult identical twins to address these aims. We will study 120 such families (1,440 individuals). Approximately one-half of these were seen 7-10 years ago, and at that time the familiar aggregation of blood pressure was apparent and due largely to genetic variation. Our re-examination will carefully re-measure blood pressure, body weight, height and skinfold thickness to evaluate the contribution of these parameters to blood pressure changes over time and the familial aggregation of blood pressure levels. We will estimate current sodium/potassium intake in all 120 families by diet food records (6 separate days), 24-hour urine collections (5 separate days) and overnight urine collections (9 separate days) to determine if sodium/potassium intake is related to the familial aggregation of blood pressure levels. These results will increase our knowledge of the relationships between blood pressure changes overtime, body weight, sodium and potassium intake and the familial aggregation of blood pressure levels, and may suggest preventive strategies to minimize the increase in blood pressure with age known to occur in certain families.